This invention deals with a monolithic integrable organ gate circuit which replaces mechanical key contacts.
As is known from the German Technical Journal "Funk-Technik" (1972), No. 17, pp 630 and 632, a problem of suppressing the bounce arises in such a gate circuit whenever the sum audio signal is taken off and produced across a load resistor common to all audio signals. As is well-known, this bounce is due to the fact that the sum audio signal is given a d.c. voltage step upon switching each individual audio frequency signal.
For eliminating this d.c. voltage step (-.DELTA.U.sub.DD) on the busbar of a load resistor, R.sub.L, it is well known to raise the supply voltage U.sub.DD during the closure of a key contact, by the amount +.DELTA.U.sub.DD, so that the mean value of this signal at the busbar will remain constant. For this purpose, and in accordance with the aforementioned reference, it is proposed to use a control circuit for increasing the output voltage in accordance with the number n of closed key contacts, to the value U.sub.DD +n.DELTA.U.sub.DD.
Such a control circuit, however, has the disadvantage that the supply voltage U.sub.DD cannot be increased at will without causing technological difficulties. For if this voltage were to be kept constant, the voltage would have to be increased externally ahead of the load resistor R.sub.L, by being controlled in accordance with the number of actuated (depressed) keys. This, however, would involve more complex and expensive circuitry.